Spot light fiber and illuminating apparatus

ABSTRACT

A spot light fiber ( 100 ) which comprises a core ( 101 ) which can transmit the light entered from an incident end towards an output end ( 102 ) and output the light from the output end, and a light leaking means ( 103 ) positioned along the peripheral direction on the external peripher face near the output end of the core; characterized in that the light leaking means is formed by using a light diffusive-transmissive light leaking film.

DETAILED DESCRIPTION OF THE INVENTION

1. Technical field

The present invention relates to a spot light fiber which can leak lightwhich has been inserted at an incident end from an output end and itsvicinity, and can be used as a light emitting body of an illuminatingapparatus of a spot light fiber type, and a spot light fiber typeilluminating apparatus using this spot light fiber.

2. Background

As known to the art, a light fiber can transmit the light inserted atthe incident end to the output end with only a small amount of lightleaking from the external peripheral face of its core, and can emit thelight with relatively high brightness at the output end. By using suchcharacteristics, the optical fiber can be used as a light emitting bodyof a light fiber type illuminating apparatus.

An illuminating apparatus of such a spot light fiber type is disclosedin Japanese Utility Model Laid-Open Publication No. 56-161704, JapanesePatent Laid-Open Publication No. 1-169802 or the like. But in anordinary light fiber, the light is emitted from the output end in anapproximately parallel light beam, so that efficient extension cannot beprovided in the illumination light and the illumination spot area cannotbe made large.

A light fiber is known which can leak light from the part other than anoutput end, i.e., the external peripheral face of the core so that thelight can be used as the illumination light. For example, in JapanesePatent Laid-Open Publication No. 4-70604, Japanese Patent Laid-OpenPublication No. 1-58482, Japanese Patent Laid-Open Publication No.6-21940 or the like is disclosed a light fiber having a lightdiffusive-reflective film adhered along the axial direction of the coreon the external peripheral face of the core.

Such a light diffusive-reflective film, normally containing lighttransmissive resin and light diffusive-reflective particles,substantially does not allow the light to transmit therethrough. Rather,the light is reflected. Namely, in such a conventional light fiber asdescribed above, a portion of light which reaches the interface betweenthe light diffusive reflective film and the core is reflected by thelight diffusive-reflective film so that the light leaks out of the corefrom the external peripheral face on the side opposite to the externalperipheral face where the light diffusive-reflective film is positioned.As described above, in addition to the output end of the core of thelight fiber, the external peripheral face also functions as a lightemitting face. The light inserted into the incident end does not leakout of the core through the light diffusive-reflective film.

When the light diffusive-reflective film is used as described above, thelight can be released along the axial direction of the core, and thelight fiber can be used in place of a linear light source such asfluorescent tube or the like. However, the light fiber with a lightdiffusive-reflective film attached to it is not suitable for spotillumination.

Since the light diffusive-reflective film is normally not lighttransmissive, the size of the light leaking part is restricted, becausethe vicinity of output end of a core which becomes a light leaking partis covered by the light diffusive-reflective film itself when the lightdiffusive-reflective film is positioned as it is near the output end ofthe core. As the result, it becomes difficult to make the illuminatedarea (i.e., spot area) large.

SUMMARY OF THE INVENTION

The present invention provides a spot light fiber which can make thearea which is irradiated by the light from the output end and thevicinity of the output end of the spot light fiber large. In anotherembodiment of the present invention, a spot light fiber typeilluminating apparatus which can make the spot area large by efficientlyusing such a spot light fiber is provided.

The present invention provides a spot light fiber which comprises a corewhich can transmit the light inserted at an incident end toward anoutput end and output the light from the output end, and a light leakingmeans positioned along the peripheral direction on the externalperipheral face near the output end of the core; characterized in thatthe light leaking means is formed by using a lightdiffusive-transmissive film. Preferably, the light leaking meanscircumscribes the core in a location adjacent the output end.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view showing one embodiment of a spot lightfiber of this invention. A spot light fiber 100 of this invention has alight leaking means 103 positioned along the peripheral direction on theexternal peripheral face near the output end 102 of the core 101. In thepresent specification, the peripheral direction is referred to as adirection normal to the axis of the core.

By using a light diffusive-transmissive light leaking film which allowsthe light to be diffused and transmitted as the light leaking means ofthe light fiber, the light leaking brightness from the outer peripheralface near the output end is efficiently improved. Accordingly, theleaked light from the light diffusive-transmissive light leaking filmand the emitted light from the output end can be efficiently irradiatedtoward the illuminated area, thereby the efficient illumination angle(for example, an angle by which brightness more than 1,500 luxes can beobtained) is expanded, and the spot area is efficiently enlarged.

FIG. 2 is a perspective view of one embodiment of a lightdiffusive-transmissive light leaking film to be used for forming a lightleaking means of a spot light fiber of this invention. In the drawing,reference numeral A shows the peripheral direction of the core.

A suitable light diffusive-transmissive light leaking film 200 to beused by this invention has:

(i) a light transmissive base part 201 having two approximately parallelmajor faces; and

(ii) a plurality of light transmissive convex parts 202 formed anderected integrally with the base part on one major face of the basepart, each convex part having approximately the same height, with a topface 203 having an adhesive property and the refractive index being 1.1or more.

The light leaking means of this invention can be formed by using thelight diffusive-transmissive light leaking film. Specifically, this isaccomplished by adhering the top face 203 of the convex part 202 of thelight diffusive-transmissive light leaking film 200 on the externalperipheral face of the core. The film and the core are positioned sothat a void 204 can be retained between the core external peripheralface and the base part of the light diffusive-transmissive light leakingfilm, and between the convex part and the convex part of the lightdiffusive-transmissive light leaking film.

When the light diffusive-transmissive light leaking film 200 is adheredon the external peripheral face of the core, the lightdiffusive-transmissive light leaking film is oriented so that thedirection A on FIG. 2 becomes normal to the axis of the core. That is,the convex part 202 of the light diffusive-transmissive light leakingfilm 200 runs perpendicular to the direction of the fiber.

Since such a light leaking means leaks the light by using the lightscattering function by the concave-convex shape of the lightdiffusive-transmissive light leaking film, the diffusing reflectionparticles are not required to be contained in the lightdiffusive-transmissive light leaking film. The light transmissive rateof the film itself can be improved as high as possible. Thus, thebrightness of the light to be illuminated through the lightdiffusive-transmissive light leaking film can be improved efficiently.

The refractive index of the convex part is normally 1.1 or more. Thepart of the light which reaches the output end and is not irradiatedfrom the external peripheral face, in case that the lightdiffusive-transmissive light leaking film would not be provided,transmits through the light diffusive-transmissive light leaking film toleak out of the core. Namely, the light that reaches the face adheredwith the concave part penetrates into the convex part and is reflectedor scattered by the interface between the void and the convex part sothat it leaks out of the core through the light diffusive-transmissivelight leaking film.

The refractive index of the convex part is preferably 1.2 through 2.5.More preferably, it is in the range of 1.3 through 2.0. When therefractive index of the convex part is 1.2 or lower, it is possible thatthe brightness of the spot will not be improved. On the other hand, whenit exceeds 2.5, the amount of the output light from the output end islowered, thereby the brightness of the illumination spot is notimproved.

The refractive index of the convex part is preferably almost the same asor larger than that of the core. The difference (Δ=F−C) between therefractive index (C) of the core and the refractive index (F) of thelight diffusive-transmissive light leaking film is normally in the rangeof −0.1 through 1.0.

The light transmission factor of the convex part is not restrictedunless the effects of this invention are not damaged. In the entire zoneof the wavelength of 400 through 800 nm, a value measured by aspectro-photometer is normally 70% or more.

A dimension of a void to be formed when the light diffusive-transmissivelight leaking film has been adhered on the external peripheral face ofthe core is not restricted unless the effects of this invention are notdamaged. For example, a distance between the top parts of two adjacentconvex parts is normally 0.001 through 500 mm, preferably in the range0.01 through 50 mm, and more preferably is 0.02 through 10 mm. Theheight of the void (interval from the core face to the bottom face ofthe concave part) is normally 0.001 through 10 mm, and is preferably inthe range of 0.01 through 5 mm.

When these void dimension is smaller than the normal range, the amountof light leaking and the spot brightness may become low. When the voiddimension is larger than the normal range, a part with the lightdiffusive-transmissive light leaking film being adhered thereto becomesbulky, thereby damaging the outer appearance of the spot light fiber.When the void dimension is too large in view of the elastic rate of theconvex part, there is a great likelihood of difficult retaining thevoid.

An area of one convex top face of the light diffusive-transmissive lightleaking film is normally 10⁻⁴ through 25 mm² and is preferably in therange of 10⁻³ through 10 mm². When the area of the concave top face is10⁻⁴ mm² or smaller, there is a little likelihood that the scatteringeffects are lowered and the brightness is lowered. When it is 25 mm² ormore, the spot area becomes too wide with a likelihood of the brightnessnear the spot enter is lowered.

Unless the effects of this invention are damaged, the lightdiffusive-transmissive light leaking film which does not have suchconcave-convex shape can be used as a light leaking means. A film havinga flat adhering face can be used which includes, for example, lighttransmissive resin and bubbles scattered within the resin. Or a film canbe used which has polymer particles scattered, having refractive indexdifferent from that of the resin, instead of the bubbles. In the case ofthe latter, the difference between the refractive index of the resin andthe refractive index of the polymer particles is normally 0.05 or more.

Illuminating Apparatus

An illuminating apparatus of this invention has a spot light fiberhaving the above characters and a light source for providing the spotlight fiber with light. The light emitted from the output end and thelight leaked through the light diffusive-transmissive light leaking filmcan be used as the illuminating light. The light emitted from the outputend can be efficiently irradiated toward the illuminated area, widen theefficient illuminating angle and efficiently enlarge the spot area.Normal lamps such as xenon lamp, halogen lamp, light emitting diode,fluorescent lamp or the like can be used as a light source. Theconsumption power of the light source is normally 10 through 300W.

Core

A fiber core of this invention is formed from the material which hastransparency enough to transmit the light inserted into the interior ofthe core from one end to the other end. It is for example made of thematerial which has a refractive index in the range of 1.4 through 2.0.Such materials include, for example, quartz glass, optical glass,polymers or the like.

While a core is made of a solid core made of the transparent material, aliquid charged type core or the like can be used with liquid ofrelatively high refractive index such as silicone gel or the like beingcharged in a flexible plastic tube can be used. In a case of the solidcore, the light diffusive-transmissive light leaking film is positionedand then, can be covered with clad to prevent the core from beingdamaged. A clad is made of a transparent material having a refractiveindex of less than that of the core.

A polymer which is a core material can be made of a light transmissivepolymer such as acrylic polymer, polymethylpenten, ethylene-vinylacetate copolymer, polyvinyl chloride, vinyl acetate-vinyl chloridecopolymer or the like. The refractive index of the polymer is normally1.4 through 1.7 and the entire ray transmitting factor is normally 80%or more. In order to give sufficient mechanical strength to theflexibility of the core itself, the polymer can be crosslinked.

A method of making the solid core will be described as follows by way ofacrylic core.

The acrylic monomer (mixture) which is a core material is filled in atube extended in a longitudinal direction and having an opening part atleast one end, and then, the mixture is heated sequentially attemperatures of a reacting temperature or more as the reaction of themixture is caused sequentially towards the opening end from another endside of the tube. Namely, the heating position is moved towards theopening end from another end side. The reaction is conducted whilepressing the mixture with a pressure gas which comes into contact withthe mixture. In order to completely finish the reaction after theheating has been finished to the opening end, it is preferable tofurther heat the whole tube for several hours.

Acrylic monomer which is a core material include, for example, (i)(meth)acrylate in which the Tg of homopolymer is higher than 0° C. (forexample, n-butyl methacrylate, methyl methacrylate, methyl acrylate,2-hydroxyethyl methacrylate, n-propyl methacrylate, phenyl methacrylateor the like), (ii) (meth)acrylate in which the Tg of homopolymer islower than 0° C. (for example, 2-ethylhexyl methacrylate, ethylacrylate, tridecyl methacrylate and dodecyl methacrylate or the like),or a mixture between (i) and (ii). In the case of the mixture, themixing weight ratio (H:L) between the (meth)acrylate (H) of the (i) andthe (meth)acrylate (L) of the (ii) is normally in the range of 15:85through 60:40. As a crosslinking agent, multifunctional monomer such asdiallyl phthalate, triethylene glycol (meth)acrylate, diethylene glycolbisallyl carbonate or the like can be added to the mixture.

The acrylic core formed as described above, can be made as a homogeneouspolymer from one end of the core to another end. It has good lighttransmissive performance and sufficient mechanical strength to theflexibility of the core body. Further, the spot light fiber becomes easyto treat by using the acrylic core. Thus, the acrylic core is suitablefor the core.

The tube to be used in the producing method is preferable to be fluoropolymer such as tetrafluoro ethylene-hexa fluoro propylene copolymer(FEP) or the like. The method of manufacturing such a flexible spotlight fiber (core) is disclosed in Japanese Patent Laid-Open PublicationNo. 63-19604.

Any sectional shape of the core in the width direction of the core willbe employed, such as circular, oval, semicircular, bow larger in areathan semicircular, unless the effects of this invention are damaged. Thediameter of the core, when the cross-section in the width direction iscircular, is normally in the range of 3 through 40 mm, and preferably 5through 30 mm.

Light Diffusive-transmissive Light Leading Film

One preferable embodiment of the light diffiusive-transmissive lightleaking film comprises, as described above,

(i) a light transmissive base part having two approximately parallelmajor faces; and

(ii) a plurality of light transmissive convex parts formed and erectedintegrally with the base part on one major face of the base part, eachconvex part having approximately the same height, with a top face havingan adhesive property and the refractive index being 1.1 or more.

The light diffusive-transmissive light leaking film may be adhered onthe core external peripheral face by using the self-adhesiveness of theconvex part or by using a light transmissive adhesive agent. As thelight transmissive adhesive agent can be used, for example, an acrylicpressure sensitive adhesive agent.

The elastic modulus of the convex part is properly decided so as toretain the void. The elastic modulus G in the 25° C. of the convex partis preferably in the range of 5×10⁵ through 1×10¹⁰ dyne/cm². When theelastic modulus is 5×10⁵ dyne/cm² or lower, the convex part flows inplasticity as time passes, thereby making it difficult to retain theshape of the void. On the other hand, when it exceeds 1×10¹⁰ dyne/cm²,the core face may be damaged in the adhering operation of the lightdiffusive-transmissive light leaking film.

When the reduction of the log₁₀G is 1.0 or less in the range of 25° C.through 125° C., in addition to the restriction of the elastic modulusG, the retaining performance of the gap formed between the lightdiffusive-transmissive light leaking film and the core can beefficiently increased. When the reduction of the log₁₀G is 1.0 orlarger, namely, when the variation in the temperature range of log₁₀ Gbecomes −1.0 or lower, the convex part may flow in plasticity as timepasses.

The elastic modulus G of the base part is not particularly restrictedto, but it is suitable to be in the range similar to that of the convexpart when the base part is formed integrally with the convex part. The“elastic modulus G” in the present specification is a value measured bythe dynamic viscoelastic method with 1 rad/second frequency, in a sheermode.

For example, acrylic polymer is used in order to form the concave partor/and the base part which has such predetermined elastic modulus. Thistype of polymer is prepared by polymerization of raw material componentsincluding, for example, alkyl (meth)acrylate, ethylenically unsaturatedacid. Also, it can be prepared by the polymerization of raw materialcomponents including acryl-modified polymerizing prepolymer or oligomersuch as urethan acrylate or the like. In addition to acrylic polymer, itcan be used rubber polymer such as silicone rubber, butyl rubber stylenerubber or the like, or polymer such as polyurethane or the like.

The convex part can be of any shape unless the effects of this inventionare damaged. Preferably the sectional shape is approximatelyrectangular. For example, the sectional shape of the convex part isrectangular 0.01 through 5 mm in width, or is trapezoidal 0.01 through 5mm in upper bottom, and 0.02 through 10 mm in lower bottom. They areeasy to give concave-convex shape as designed, which provides withsufficient area of contact face, and is easy to work.

The base part is made of a material which is the same as the convex partincluding crosslinked acrylic polymer. The base part is preferable to beformed integrally with the concave part although the lightdiffusive-transmissive light leaking film can be prepared by splicingwith the base part and the concave part being prepared separately. Thereason is that it is easy to give concave-convex shape as designed.

The thickness of the base part is normally 0.01 through 2 mm, preferably0.05 through 1 mm, and more preferably 0.1 through 0.5 mm. When itbecomes too thin, base part may break during use. When it becomes toothick, the light diffusive-transmissive light leaking film becomesvoluminous, thereby damaging the outer appearance when it is positionedon the core face.

The voids (concave parts) between mutually adjacent convex parts arepositioned to form regularly geometrical patterns across theapproximately entire face of one major face of the base part. Suchgeometrical patterns are, for example, lattice pattern, zigzag, parallelstripe (a plurality of stripes are parallel) or the like. The number ofthe arrangements of the concave parts per unit area is normally 0.3through 50/cm².

The concave parts can have various different shapes. For example,geometrical space such as circular cylinder, semi-circular cylinder,prism, pyramid, circular cone, semicircular cone, truncated pyramid,circular truncated cone, spherical segment, ellipsoidal and so on can beprovided. The concave part can adopt the composite shape of one type ortwo types or more selected from a group consisting of these shapes. Thevoid between the concave part and the core face can be closed space oropen space which communicates with the outer space.

The light diffusive-transmissive light leaking film is positioned sothat the bottom face of the concave part may be away from the core, withthe top face of the convex part being adhered on the external peripheralface of the core. When the shape or the position (namely, pattern) ofthe concave part has anisotropy within the horizontal face, it ispreferable to position the light diffusive-transmissive light leakingfilm so as to leak the light with the highest brilliance towards theillumination spot. For example, when the concave part has a parallelstripe pattern, the length direction of these stripes is preferable tobe positioned so as to go along the peripheral direction of the core (tobe orthogonal to the axis of the core).

When a light leaking means is formed by using such a lightdiffusive-transmissive light leaking film, the axial length of the lightleaking means is normally in the range of 3 through 50 mm, preferably 5through 40 mm, and more preferably 10 through 30 nm. When the axiallength of the light leaking means is smaller than the normal range, thelight leaking brightness becomes low, and the efficient illuminationangle (for example, an angle by which brightness of more than 1,500 luxcan be obtained) cannot be made large. On the other hand, when it islarger than the normal range, the brightness of the output light fromthe output end becomes lowered so that there is a likelihood that thebrightness near the spot center cannot be increased.

Such a light diffusive-transmissive light leaking film as describedabove is described in commonly assigned U.S. patent application Ser. No.08/755767.

Preparation of Light Diffusive-transmissive Light Leaking Film

The light diffusive-transmissive light leaking film can be prepared byusing, for example, acrylic polymer. The acrylic polymer is preferableto be a crosslinked one. The crosslinked acryl polymer can be preparedby polymerization of the raw material components substantially composedof, for example, alkyl (meth)acrylate, ethylenically unsaturated acid,and crosslinking agent monomer having two (meth)acrylic radicals or morewithin the molecule.

The alkyl (meth)acrylate (The wording means “alkyl acrylate” or “alkylmethacrylate.) includes those in which alkyl group is either of methyl,ethyl, isopropyl, butyl, isobutyl, 2-ethylhexyl, isooctyl, lauryl,stearyl, cyclohexyl, isobornyl, 2-hydroxyethyl, 2-hydroxypropyl,methoxyethyl, ethoxyethyl, dimethylaminoethyl, decylamonoethyl,glycidyl. The alkyl (meth)acrylate may be used alone or in combinationof more than two.

The ethylenically unsaturated acid preferably includes (meth)acrylicacid (The wording means “acrylic acid” or if “methacryl acid”). The(meth)acrylic acid efficiently increases the cohesion force of theacrylic polymer to improve the shape retaining property and mechanicalstrength of the convex part. As another ethylenically unsaturated acidis used one type of β-hydroxyethyl carboxylic acid, itaconic acid,maleic acid, fumaric acid, or mixture of two types or more selected fromthem.

The blending proportion between alkyl (meth)acrylate (A) andethylenically unsaturated acid (E) is selected so that the elasticmodulus of the convex part (11) is in the predetermined range, butpreferably is in the range of A:E=80:20 through 99:1.

The crosslinking agent monomer having two (meth)acrylic radicals or morewithin a molecule preferably includes 1,6-hexanediol diacrylate. The1,6-hexane diol diacrylate efficiently increases the crosslinkingdensity of acrylic polymer so as to improve the shape retaining propertyand the mechanical strength of the convex part for better balancing. Thecontent of the crosslinking agent monomer is normally in the range of0.5 through 5% by weight based on the entire raw material components.

Acryl modified prepolymer oligomer such as urethane acrylate or thelike, instead of the ethylenically unsaturated acid and/or crosslinkingagent monomer, can be used to prepare the crosslinked acrylic polymer.When such a material is used, the elastic modulus of the convex part canbe improved efficiently and the shape retaining property of the convexpart can be easily improved.

The acrylic polymer, by using a raw material component which includesabove described each component as a starting material, can be obtainedthrough polymerization with heat or irradiation rays such as ultravioletrays, electron beam or the like. For example, the raw materialcomponents is contacted with a mold having the predetermined geometricconfiguration, then it is polymerized (including crosslinking) on themold to form a light diffusive-transmissive light leaking film. In thiscase, the raw material components including no crosslinking agentmonomer may be by partially polymerized in advance to prepareviscosity-adjusted partial polymerized syrup. Then the mixture betweenthe syrup and the crosslinking agent monomer is put into contact withthe mold, the polymerizing and crosslinking can be completed. In orderto efficiently operate the polymerization, a polymerization initiatorcan be used. Such a polymerizing initiator is, for example, benzophenoneoptical initiator (for example, Irgacure 651™ made by Ciba Geigi Co.) orthe like.

In one preferred embodiment of this invention, the light diffusionpermeability light leaking film is produced by the following replicationmethod.

The raw material components containing the above described material at apredetermined proportion and the polymerization initiator are put into astirring apparatus to conduct an ultraviolet ray polymerizing operationwhile stirring. At this stage, the polymerization is conducted partiallyto prepare the partially polymerized syrup so that the viscosity maybecome a range of 100 through 100,000 cps. On addition of thecrosslinking agent, a predetermined amount of the crosslinking agentmonomer and the light initiator are added to the syrup and mixed untilit becomes homogeneous to prepare the raw material components of thelight diffusive-transmissive light leaking film. The stirring apparatusis normally purged with inert gas such as nitrogen gas or the like.

A mold for forming a light diffiusive-transmissive light leaking filmhaving the predetermined geometric configuration (concave-convex) isprepared as follows. A positive mold composed of relatively hard,plastic or metal, having the predetermined geometric configuration isprepared. Acrylic, polycarbonate or the like are suitable plasticmaterials. A releasing resin is put into contact with the positive mold,and the releasing resin is hardened with ultra violet rays. It isreleased from the positive mold, so as to make a negative mold. Aconcrete example of a positive mold like this include “ACRYSUNDAY PLATE”series made by Acrysunday (Ltd.) Company. A concrete example of thereleasing resin include the molding silicone SE9555 made by Toray-DowCorning Ltd.

The raw material components of the light diffusive-transmissive lightleaking film is put into contact with the negative mold and atransparent releasing film is placed on the components. At this time,when the components are polymerized and cross-linked the negative moldand the releasing film are positioned at a predetermined space so as toform a part which becomes a base part of the light diffusionpermeability light leaking film and a part which becomes a convex part.In this condition, the ultraviolet rays are applied through thereleasing film to complete the hardening reaction, and the negative moldand the releasing film are removed, thereby a light diffusionpermeability light leaking film composed of the components hardened isobtained.

The releasing film is used for cutting off oxygen, and for making flatanother major face of the light diffusive-transmissive light leakingfilm. Normally a flexible plastic film such as polyester (PET) or thelike is used as the releasing film.

In order to decide the thickness of the base part, the following methodcan be adopted. Namely, the method comprises steps of pouring an excessof raw material components onto the negative mold, covering on it with arelease film, so as to form laminated materials containing thecomponents, and then, passing the laminated material through the gap ofknife coater having a gap fixed to the given interval, discharging theexcess portion of the raw material component from the edge part of thelaminated material to adjust the thickness and the flatness of a partwhich becomes a base part.

When the ultraviolet rays are used as described above, the wavelength ofthe ultraviolet ray is in the range of 300 through 400 nm, and theilluminating intensity is in the range of 330 through 1,000 J/cm².

The light diffusive-transmissive light leaking film may contain varioustypes of additives unless the effects of this invention are damaged. Theadditives are, for example, tackifier, plasticizer, ultraviolet rayabsorbing material, antioxidant, coloring material, filler or the like.

A plastic film of non-tackiness can be laminated on the major facehaving no convex part of the base part. The light permeability factor ofsuch a plastic film should be 80% or more at a value measured by aspectro-photometer in the entire zone of the wave length of 400 through800 nm.

EXAMPLES

Although the present invention will be further described concretely bythe following examples, the invention is not restricted by them.

Example 1

A spot light fiber of this Example was made from a combination of a coreand a light diffusive-transmissive light leaking film to be describedhereinafter.

(1) Core

A core part of a light fiber “(Commodity Number) EL700” made by LumenyteCo., Ltd. was used. It is a solid core of 1 m in core length, 18 mm indiameter of the core section (circular), and 1.49 in refractive index.

(2) Light diffusive-transmissive light leaking film

A partially polymerized syrup by ultraviolet ray polymerization, wasprepared from raw material components composed of 90 parts by weight ofisooctyl acrylate, and 10 parts by weight of acryl acid, and sparecomponents composed of 0.1 parts by weight of irgacure 651 as a lightstarting agent. To the syrup are added 1 parts by weight of1,6-hexanediol diacrylate and 0.2 parts by weight of additional lightstarting agent (irgacure 651) as a crosslinking agent monomer. They aremixed until they became homogeneous to prepare the raw materialcomponents for the light diffiusive-transmissive light leaking film.

The light diffusive-transmissive light leaking film of this example iscomposed of the ultraviolet hardened raw material components, and it wasmade by using the raw material components and a method of using thecasting mold. As a releasing film was used PET film “(Trade Mark)Lumirror 50T (50 μm thick) made by Toray Co., Ltd.

The light diffiusive-transmissive light leaking film of this example hada base part and a plurality of convex parts of approximately the height,and formed integrally with the base part with the concave-convexconfiguration being a parallel stripe. The sectional area of the concavepart cut with a face vertical to the parallel stripe was approximately0.4 mm², and the width of the top of the convex part was approximately0.5 mm. The thickness of the base part was 0.2 mm. Further, the concavepart was positioned at a proportion of five/cm.

The measured value of the elastic modulus G of the convex part of thelight diffusive-transmissive light leaking film was measured under theabove described conditions by using dynamic analyzer “model number: RDAII” made by Leometrics Co. A sample retainer to be used for measuringwas a parallel plate of 7.9 mm in diameter. The elastic modulus G was6.7×105 dyne/cm², and tackiness was proper. Log₁₀G change (reduction)was calculated with variation values with G at 25° C. as a reference,which was read from viscoelastic spectrum obtained in the range of 25°C. through 125° C. Changes in log₁₀G was zero. The lighttransmissibility of the convex part measured by a spectrophotometer wasapproximately 80%, and the refractive index of the convex part and thebase part was 1.50.

The light diffiusive-transmissive light leaking film was slit along adirection parallel to the parallel stripe to a tape form of 56.5 mm inlength (dimension in the length direction of the parallel stripe) and of5 mm in width (dimension in a direction vertical to the length directionof the parallel stripe, i.e., dimension of the axial direction). Then,the side of convex part was directed to the core, and it was adhered onthe external peripheral face near the output end, so that the peripheraldirection of the core agrees with the stripe length direction of thelight diffusive-transmissive film, thereby the spot light fiber of thepresent Example was made. Namely, the parallel stripes were positionedvertical to the axis of the core. The void corresponding to the concavepart of the light diffusive-transmissive light leaking film was retainedin shape and dimension even after five months since it was adhered onthe core.

Comparative Example 1

A light fiber used as a core in the Example 1 without the lightdiffusive-transmissive light leaking film was made to a spot light fiberin this Example.

Evaluation of Lightness

The lightness of the illuminated area of the spot light fiber in theExample 1 and the comparative Example 1 each being prepared in the abovedescribed manner was evaluated as follows. As a illurninometer was useda lumino meter “(Commodity Number) T-1H” made by Minolta (Ltd.,) Co. Asa light source was used a halogen lamp (“Commodity Number: JCR-30W” madeby Iwasaki Electricity (Ltd.) Co. of 30W with a reflection mirrorattached to it.

FIG. 3 is an arrangement view of a sample and a apparatus in thelightness evaluating test of the spot light fiber of this invention. InFIG. 3, the numbering 301 is a light source, 302 is a spot light fiber,the symbol L is the width of a spot light fiber, the symbol θ is amaximum angle (illumination angle) by which the lightness more than1,500 luxes is obtained. point A and point B show the measured positionsof the lightness.

As shown in FIG. 3, a spot light fiber was positioned in parallel to thefloor face to introduce the light into the core from the incident end,and the light was applied at point A of the wall face (vertical to thefloor face) away 15 cm from the output end in a direction parallel tothe core. An area of the illumination spot including point A was seenlarger in the Example 1, by comparison with the comparative Example 1.

The lightness at point A is 16,400 luxes in-the Example 1 and 16,300luxes in the comparative Example 1. They were almost the same. But thelightness at point B where it is away 15 cm from the external peripheralface near the output end of the core in a direction vertical to thefloor face, was 1,280 luxes in the Example 1, and 1,100 luxes in thecomparative Example 1. Further, an illumination angle (θ ) by which thelightness more than 1,500 luxes could be obtained was 0 through 80° inthe Example 1 and 0 through 60° in the comparative Example 1.

Example 2

The spot light fiber of this Example was made as in the Example 1,except that the width (dimension in the axial direction) of the lightdiffusive-transmissive light leaking film was changed to 15 mm.

The lightness was measured as in the Example 1. It was found out thathigh lightness was obtained in the illumination angle (θ) of 0 through90° with the lightness at point A being 16,200 luxes, and the lightnessat point B being 1,610 luxes.

Example 3

The spot light fiber of this Example was made as in the Example 1,except that the width (dimension in the axial direction) of the lightdiffusive-transmissive light leaking film was changed to 25 mm.

The lightness was measured as in the Example 1. It was found out thathigh lightness was obtained in the illumination angle (θ) of 0 through90° with the lightness at point A being 16,400 luxes, and the lightnessat point B being 1,850 luxes.

From the results of the Examples 1 through 3, it was found out that thelightness of a certain circular spot in the illuminated area could beincreased by increasing of the width (dimension of the lightdiffusive-transmissive light leaking film in the axial direction of thecore) of the light diffusive-transmissive light leaking film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A perspective view showing one Example of a spot light fiber ofthis invention.

FIG. 2 A perspective view showing one Example of the lightdiffusive-transmissive light leaking film to be used to form the lightleaking means of the spot light fiber of this invention.

FIG. 3 An arrangement view of a sample and an apparatus in the lightnessevaluating tests of the spot light fiber of this invention.

What is claimed is:
 1. A spot light fiber comprising: a core that cantransmit the light insert at an incident end toward an output end andemit the light from the output end; a light release element comprising alight diffusing film wrapped around the peripheral face of the lightfiber at the output end, said light release element comprising a lighttransmissive base part having two approximately parallel major faces;and a plurality of light transmissive light extracting convex partsformed on one major face of said base part the outer surfaces of saidconvex portions being adhesively attached to said light fiber andforming gaps between said light fiber and said basic part between saidconvex parts.
 2. A spot light fiber according to claim 1 wherein each ofsaid convex portions has approximately the same height.
 3. A spot lightfiber according to claim 1 wherein said convex portions run transverseto the axis of said light pipe.